Sinter joining method and sintered composite member produced by same

ABSTRACT

A sinter-joining method for forming a sinter of high quality at low cost and a sintered composite member produced by the sinter-joining method. 
     A tubular copper-base material is forced into a tubular iron-base material and these materials are sintered at temperatures equal to and higher than 600° C. so that the copper-base material expands and pressure-joins to the iron-base material. Then, the materials are sintered at temperatures equal to and higher than 850° C. so that the compactness of the copper-base material is increased. Through these steps, the sintered composite member containing the copper-base material joined to the inside of the iron-base material is obtained.

TECHNICAL FIELD

The present invention relates to a sinter-joining method and a sinteredcomposite member produced by this method. More particularly, theinvention relates to a sinter-joining method for joining a copper-basematerial to an iron-base material through sintering and a sinteredjoined member produced by this method.

BACKGROUND ART

For forming an integral body in which a copper-base material is receivedwithin the bore of a tubular iron-base material, one of the followingprior art techniques is generally used.

(1) Casting: A molten copper-base material is cast into the bore of aniron-base material.

(2) Diffusion joining: A copper-pipe material is first inserted orforced into the bore of an iron-base material. Then, these materials areheated and diffusion-joined by utilizing the difference between theircoefficients of thermal expansion and the transformative contraction ofiron.

(3) Brazing: A copper-base pipe material is first inserted into the boreof an iron-base material. Then, a brazing filler metal is heated andapplied in the gap between the iron-base material and the copper-basepipe material so that the filler metal penetrates into the gap toestablish a bond between the iron-base material and the copper-base pipematerial.

These prior art methods, however, suffer from their inherent problems.The first method (1) has the problems that: (i) the use of large amountsof flux in order to achieve improved bonding ability harms the workingenvironment; and (ii) excess copper-base material needs to be cast,which leads to poor yield, considerable amounts of processing in thepost treatment subsequent to casting, and consequently, high cost.

The following problems have been encountered by the second and thirdmethods (2), (3). (i) Unless the diameter and surface roughness of thebore of the iron-base material and the outside diameter and surfaceroughness of the copper-base pipe material are adjusted with highprecision, bonding rate will vary to a considerable extent and thepercentage of defective products will increase. Supervision for ensuringsuch absolute precision incurs additional cost. (ii) Materials that canbe used for forming the copper-base pipe material are limited and theproduction of the copper-base pipe material is expensive.

Another known technique is sinter-joining in which a tubular copper-basematerial is forced into the bore of a tubular iron-base material and thematerials are wholly heated and joined to each other to produce anintegral body. In this method, a means such as a jig is used forpressurizing the copper-base material in its expanding direction frominside in order to prevent defective joining due to the shrinkage of thecopper-base material. However, it is difficult to ensure high bondingquality with this method because of the difficulty in uniform pressuretransmission.

The invention has been made for the purpose of overcoming the foregoingproblems and one of the objects of the invention is therefore to providea sinter-joining method capable of achieving high bonding quality injoining a copper-base material to an iron-base material by sinteringwithout incurring additional cost. Another object of the invention is toprovide a sintered composite member produced by this method.

DISCLOSURE OF THE INVENTION

The first object can be accomplished by a sinter-joining method forjoining a copper-base material to an iron-base material according to theinvention, the method comprising the steps of:

(a) heating the copper-base material, which is composed of at leastthree components including one or more metals and/or semi-metallicelements which have ability to give expansibility, in contact with theiron-base material at temperatures equal to and higher than 600° C. fora specified time so that the copper-base material expands and joins tothe iron-base material, and

(b) further heating the copper-base and iron-base materials attemperatures equal to and higher than 800° C. to increase thecompactness of the copper-base material.

According to the invention, the copper-base material can be firmlyjoined to the iron-base material by heating them for a specified time attemperatures equal to and higher than 600° C. at which the expandingbehavior of the copper-base material is observed. Therefore, whencompacting of the copper-base material is promoted by sintering attemperatures equal to and higher than 800° C. in the subsequent step,the copper-base material does not shift off the surface of the iron-basematerial nor separate from the iron-base material, so that excellentbonding quality can be ensured. In the sinter-joining method accordingto the invention, joining of the copper-base material to the iron-basematerial involves only temperature control and therefore no special costis incurred.

According to the sinter-joining method of the invention, the iron-basematerial is a tubular iron-base member and the copper-base material is atubular copper-base member having an outside diameter that issubstantially equal to or slightly smaller than the diameter of the boreof the tubular iron-base member. The tubular iron-base member and thetubular copper-base member are heated at temperatures equal to andhigher than 600° C. as set forth earlier, while the latter beinginserted in the bore of the former. With this arrangement, the tubularcopper-base member can be joined to the inside of the tubular iron-basemember.

In the sinter-joining method of the invention, the copper-base materialcontains a Cu--Sn component and a metal and/or semi-metallic elementwhich stabilizes the β phase of the Cu--Sn alloy or a phase similar tothe β phase of the Cu--Sn alloy, as an element for promotingexpansibility. The addition of such an element enhances the expandingbehavior of the copper-base material, which establishes a stronger bondbetween the copier-base material and the iron-base material. The elementfor stabilizing the β phase or a phase similar to the β phase may be oneor more elements selected from the group consisting of Al, Si, Ga, Be,In, Sb, Zn, Ti, Zr, Fe, Ni, Mn, Cr, and Co.

It is desirable to add an element which inhibits the stabilizingfunction of the element for stabilizing the β phase or a phase similarto the β phase. The purpose for adding such element is to encouragecompacting of the copper-base material when the behavior of thecopper-base material is transited from expanding state to thecontracting state by heating the copper-base material to temperaturesequal to and higher than 800° C. The element for inhibiting thestabilizing function may be one or more elements selected from the groupconsisting of Ti, Pb, Zn, P, Sb, Ag, and In, Ni, Co, Mn, Fe and Cr.

The second object can be accomplished by a sintered composite memberproduced by joining the copper-base material to the iron-base materialby sintering with the above-described sinter-joining method according tothe invention.

Other objects of the present invention will become apparent from thedetailed description given hereinafter. However, it should be understoodthat the detailed description and specific examples, while indicatingpreferred embodiments of the invention, are given by way of illustrationonly, since various changes and modifications within the spirit andscope of the invention will become apparent to those skilled in the artfrom this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) and 1(b) are cross sectional views of joining membersaccording to the invention.

FIG. 2 is a graphical representation of the expanding/contractingbehavior of samples according to a first embodiment of the invention.

FIG. 3 is a graphical representation of the expanding/contractingbehavior of samples according to the first embodiment.

FIG. 4 is a graphical representation of the expanding/contractingbehavior of samples according to the first embodiment.

FIG. 5 is a graphical representation of the expanding/contractingbehavior of samples according to the first embodiment.

FIG. 6 is a graphical representation of the expanding/contractingbehavior of samples according to a second embodiment of the invention.

FIG. 7 is a graphical representation of the expanding/contractingbehavior of samples according to the second embodiment.

FIG. 8 is a graphical representation of the expanding/contractingbehavior of samples according to the second embodiment.

FIG. 9 is a graphical representation of the expanding/contractingbehavior of samples according to the second embodiment.

FIG. 10 is a graphical representation of the expanding/contractingbehavior of samples according to the second embodiment.

FIG. 11 is a graphical representation of the expanding/contractingbehavior of samples according to the second embodiment.

FIG. 12 is a graphical representation of the expanding/contractingbehavior of samples according to the second embodiment.

FIG. 13 is a graphical representation of the expanding/contractingbehavior of samples according to the second embodiment.

FIG. 14 is a graphical representation of the expanding/contractingbehavior of samples according to the second embodiment.

FIG. 15 is a graphical representation of the expanding/contractingbehavior of samples according to the second embodiment.

FIG. 16 is a graphical representation of the expanding/contractingbehavior of samples according to the second embodiment.

FIG. 17 is a graphical representation of the expanding/contractingbehavior of samples according to the second embodiment.

FIG. 18 is a graphical representation of the expanding/contractingbehavior of samples according to the second embodiment.

FIG. 19 is a graphical representation of the expanding/contractingbehavior of samples according to the second embodiment.

FIG. 20 is a graphical representation of the expanding/contractingbehavior of samples according to the second embodiment.

FIG. 21 is a graphical representation of the expanding/contractingbehavior of samples according to the second embodiment.

FIG. 22 is a graphical representation of the expanding/contractingbehavior of samples according to the second embodiment.

FIG. 23 is a graphical representation of the expanding/contractingbehavior of samples according to the second embodiment.

FIG. 24 is a graphical representation of the expanding/contractingbehavior of samples according to the second embodiment.

FIG. 25 is a graphical representation of the expanding/contractingbehavior samples according to the second embodiment.

FIG. 26 is a graph for explaining the emergence of a β phase in samples.

FIG. 27 is a graph for explaining the volume of expansion required.

FIG. 28 is a graph for explaining the principle of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to the accompanying drawings, the sinter-joining methodand sintered composite member of the invention will be hereinafterexplained.

First Embodiment

Cu20Sn, Sn atomized powder, TiH, Pb atomized powder, Cu8P, graphite,phosphor iron (27% P), SiO₂, Al₂ O₃, ZrO₂, Si₃ N₄ and SiC were addedsingly or in combination in the weight percentages as enumerated inTable 1 to an electrolytic Cu powder to prepare copper-containing powdermixtures. A pressure of 4 t/cm² was applied to each powder mixturethereby to form a thin-walled tubular compact body (i.e., tubularcopper-base member) as shown in FIG. 1(a) which had an outside diameterof 25.0 (+0.0, -0.05)mm, inside diameter of 20 mm and height of 20.0 mm.Bottom-closed (blind bored) tubular bodies (i.e., tubular iron-basemembers) each having an outside diameter of 25.0(+0.2, -0.0)mm and depthof 25 mm as shown in FIG. 1(b) were made from SCM440H steel. Thethin-walled tubular compact body made from each powder mixture wasforced into the blind bore of each bottom-closed tubular body. Thesecombined bodies were heated in an atmosphere (dew point=-50° C. or less)of ammonia cracked gas, while elevating temperature at a rate of 5°C./minute. The bodies were kept at sintering temperature for 15 minutesand then cooled with a temperature dropping rate of 30° C./minute ormore thereby to prepare a sintered composite member corresponding toeach powder mixture.

                                      TABLE 1                                     __________________________________________________________________________    Cu20Sn SnAt                                                                             TiH                                                                              Pb Cu8P                                                                              C(Gr)                                                                             Fe27P                                                                             SiO.sub.2                                                                        Al.sub.2 O.sub.3                                                                  ZrO.sub.2                                  __________________________________________________________________________    1 0    0  6.0                                                                              0                                                                2 0    0  10.0                                                                             0                                                                3 0    0  6.0                                                                              5.0                                                              4 0    0  10.0                                                                             10.0                                                             5 10   0  6.0                                                                              5.0                                                              6 10   2.0                                                                              6.0                                                                              5.0                                                              7 25   5.0                                                                              0  5.0                                                              8 25   5.0                                                                              0.5                                                                              5.0                                                              9 25   5.0                                                                              1.0                                                                              5.0                                                              10                                                                              25   5.0                                                                              2.0                                                                              5.0                                                              11                                                                              25   5.0                                                                              3.0                                                                              5.0                                                              12                                                                              25   5.0                                                                              1.0                                                                              5.0                                                                              6.5                                                           13                                                                              25   5.0   5.0    1.0                                                       14                                                                              25   5.0                                                                              2.0                                                                              5.0    0.2                                                       15                                                                              25   5.0                                                                              0.5                                                                              5.0    0.5                                                       16                                                                              25   5.0                                                                              2.0                                                                              5.0    1.9                                                       17                                                                              25   5.0   5.0        1.0                                                   18                                                                              25   5.0   5.0        5.0                                                   19                                                                              25   5.0                                                                              0.5                                                                              5.0        1.0                                                   20                                                                              25   5.0   5.0            1.5                                               21                                                                              25   5.0                                                                              0.5                                                                              5.0            0.5                                               22                                                                              25   5.0                                                                              0.5                                                                              5.0            1.5                                               23                                                                              25   5.0   5.0               1.0                                            24                                                                              25   5.0                                                                              0.5                                                                              5.0               1.0                                            25                                                                              25   5.0   5.0                   1.0                                        26                                                                              25   5.0                                                                              0.5                                                                              5.0                   1.0                                        27                                                                              25   5.0                                                                              0.5                                                                              15.0                                                             __________________________________________________________________________

Expansion/contraction resulted from a single addition of TiH and thelower limit amount of TiH!

The additives shown in FIGS. 2 and 3 were added singly or in combinationto a base powder material containing 25 wt % of Cu20Sn, 5 wt % of Snatomized powder, 5 wt % of Pb atomized powder and the remaining part ofelectrolytic Cu powder (CE15) to prepare powder mixtures. Each powdermixture was formed into a thin-walled tubular compact body which was thesame as described previously and each thin-walled tubular compact bodywas heated with temperature being elevated from 790° C. to measure itsdimensional change rate. The results are shown in FIGS. 2 and 3. In thegraph of FIG. 2, the amount (wt %) of each additive used is plotted onthe abscissa and the dimensional change rate (%) is plotted on theordinate. In the graph of FIG. 3, "Gr" represents graphite, and"2Ti--1Gr", for example, means that 2 wt % of Ti and 1 wt % of graphitewere added.

It is understood from FIG. 2 that when TiH was added alone, theexpansion of the thin-walled tubular compact body was significant in thelow temperature region (e.g., 790° C.) so that the thin-walled tubularcompact body was pressure joined to the surface of the bore of thebottom-closed tubular body, due to its self-expansion. It is understoodfrom FIG. 3 that the thin-walled tubular compact body formed from thepowder mixture containing TiH alone as an additive was significantlycontracted by sintering and the sinter had good compactness in the hightemperature region (e.g., 820° C.).

Of the powder mixtures, the powder mixture containing 0.5 wt % of TiHallowed the thin-walled tubular compact body to be fitted in thebottom-closed tubular body with substantially no clearance therebetweenso that a good joining condition was achieved.

The upper limit amount of TiH and the lower limit amount of Sn, theeffect of the coexistence of Pb and Sn!

Sn was added in amounts of 0.2 wt % and 4 wt % respectively to a basepowder material containing 6 wt % of Ti, 5 wt % of Pb, the remainingpart of Cu to prepare powder mixtures which were respectively formedinto a thin-walled tubular compact body having the same dimensions asdescribed earlier. The dimensional change rates of the thin-walledtubular compact bodies during sintering ware measured. FIG. 4 shows theresults of the measurements. As seen from FIG. 4, in the presence of 4wt % of Sn, the sinter expanded in the low temperature region andremarkably contracted in the high temperature region. From an economicalviewpoint, the upper limit amount of TiH is preferably about 7.0 wt %.

Pb was added in amounts of 0.5 wt % and 10 wt % respectively to a powdermaterial containing 6 wt % of Ti and the remaining part of Cu to preparepowder mixtures for forming a thin-walled tubular compact body. Thedimensional change rates of the thin-walled tubular compact bodiesduring sintering were measured and the results of the measurements areshown in FIG. 5.

As understood from FIG. 5, the addition of Pb does not only contributeto an improvement in bonding ability but also has the effect ofenhancing contraction so that the thin-walled tubular compact bodycontaining 10 wt % of Pb remarkably contracts in the high temperatureregion in spite of the absence of Sn. However, when taking into accountthe risk of evaporation of Pb in conjunction with environmentalproblems, it is desirable to use Sn in combination with Pb therebyrestricting the final sintering temperature. Bonding quality can bestabilized simply by adding PB and particularly, the addition of 15 wt %of Pb ensures satisfactory practicability by permitting the thin-walledtubular compact body to have a shearing strength of 7 kg/mm² or more atits joint surface with the above-described bottom-closed tubular bodymade from an iron-base material. In view of environmental problems andserviceability, the maximum amount of Pb is about 15 wt %.

Single addition of graphite and ceramic particle materials and theeffect of addition of these materials in combination with TiH!

As seen from FIGS. 2 and 3, in the case of single addition of graphite,virtually no expansion was observed in the low temperature region but itoccurred as sintering temperature increases, so that the sinter couldnot obtain sufficient compactness although it had bonding ability. Thereason for this is considered to be that the poor wettability ofgraphite relative to the Cu--Sn--Pb phase generated during liquid phasesintering adversely affects the expansibility of the sinter. Addition ofTiH or Zr together with graphite is therefore considered suitable toimprove the wettability of graphite. As Zr works on Cu similarly to Ti,Zr may be used in the invention although the amount of Zr to be added islimitative.

It is understood from FIGS. 2 and 3 that addition of a ceramic particlematerial such as SiO₂, Al₂ O₃ or ZrO₂ alone contributes to thecontractibility of the sinter rather than the expansibility of thesinter in the low temperature region. This fact is confirmedparticularly by the cases where Al₂ O₃, Mo (see the Second Embodimentdescribed later) or phosphor iron is added.

Where 0.5 wt % of TiH was added in addition to each kind of ceramicparticles (i.e., SiO₂, Al₂ O₃ or ZrO₂), the increased contractibilitydue to the addition of the ceramic particles is restricted while theeffect of TiH is enhanced so that the bonding ability of the sinter isincreased. This phenomenon is noticeable particularly in the case of Al₂O₃ addition. As this phenomenon is common to Al₂ O₃, SiO₂ and ZrO₂, itis conceivable that it would be observed in addition of other ordinaryceramic materials.

It was observed that the contraction of the sinter was promoted bysingle addition of the above material without use of TiH except for thecase of Gr and therefore the effect of addition of TiH was proved.

As obvious from the case of single addition of 1 wt % Gr, when Gr wasadded without TiH, the sinter was not sufficiently densified in the hightemperature region. This resulted in unsatisfactory shearing strengthwhich ranged from 3 to 5 kg/mm². On the other hand, when Gr was addedtogether with 2.0% TiH, a shearing strength of 15 to 20 kg/mm² could beachieved. As understood from the comparison between these cases, thestrength obtained by single addition of Gr is considerably poor. Evenwhen Ti is added to join with cast iron which contains graphite whichinhibits a bond between the joining materials, Ti reacts with graphite,forming a compound phase TiC. In view of this fact, the preferableamount of Ti is 0.2 wt % or more, for ensuring stable bonding abilityand bonding strength. Insufficient expansion in the low temperatureregion can be compensated by further addition of Al, Si or Zn (describedlater). Addition of Ti in an amount of 0.2 wt % or more has theadvantage of perfectly preventing foaming during sintering of a Cu--Snalloy.

The effect of addition of Cu8P!

When adding P in the form of a Cu--P alloy, P in an amount of 0.1 wt %or more has a remarkable effect because it significantly improves theflowability and wettability of a liquid phase which is generated in asmall amount. However, addition of large amounts of P leads tobrittleness. Therefore, the maximum amount of P is preferably about 1.0wt %.

Single addition of Mo or W also leads to significant contraction butwhen Mo or W is added in combination with TiH, considerableexpansibility can be achieved. Therefore, these elements are worthconsideration.

Second Embodiment 2

Cu20Sn, Sn atomized powder, TiH, Pb atomized powder, Si stamped powder,Al atomized powder, NiAl stamped powder, Ni₂ Al₃ stamped powder, Fe10Alatomized powder, Cu30Zn atomized powder, carbonyl Ni, carbonyl Co, Mo,W, TiSi stamped powder, Mn stamped powder, and Cr stamped powder wereadded singly or in combination to prepare copper-containing powdermixtures. Similarly to the first embodiment, a thin-walled tubularcompact body (i.e., tubular copper-base member) was made from eachpowder mixture and bottom-closed tubular bodies (i.e., tubular iron-basemembers) were made from SCM440H steel. Each thin-walled tubular compactbody was forced into each bottom-closed tubular body and then thesebodies were sintered in the same way as described in the firstembodiment to form sintered composite members corresponding to therespective powder mixtures.

                                      TABLE 2                                     __________________________________________________________________________    Cu20Sn SnAt                                                                             TiH                                                                              Pb Si                                                                              Al                                                                              Ni                                                                              Co                                                                              Mo W NiAl                                                                             Ni.sub.2 Al.sub.3                                                                 Fe10Al                                    __________________________________________________________________________    1 25   5.0                                                                              0.5                                                                              5.0                                                              2 25   5.0                                                                              1.0                                                                              5.0                                                              3 25   5.0                                                                              2.0                                                                              5.0                                                              4 25   5.0                                                                              3.0                                                                              5.0                                                              5 25   5.0   5.0                                                                              1.0                                                           6 25   5.0   5.0  0.5                                                         7 25   5.0   5.0    2.0                                                       8 25   5.0   5.0      2.0                                                     9 25   5.0   5.0        2.0                                                   10                                                                              25   5.0   5.0           2.0                                                11                                                                              25   5.0   5.0             1.0                                              12                                                                              25   5.0   5.0             3.0                                              13                                                                              25   5.0   5.0                3.0                                           14                                                                              25   5.0   5.0                    3.0                                       __________________________________________________________________________

In order to check the effect of each of the above additives, thedimensional change rate of the thin-walled tubular compact body madefrom each powder mixture was measured when sintered at 820° C. Theresults of the measurements are shown in FIGS. 6 and 7. As seen fromthese figures, expanding behavior was observed in the sinter made fromthe powder mixture containing Si, Al, TiH or an intermetallic compoundcontaining Si, Al or TiH. It is also understood that Mo and W have theeffect of enhancing contractibility and therefore the degree ofsintering, like the ceramic particle materials disclosed in the firstembodiment, while Ni and Co do not give virtually no effect on thedimensional change rate.

It is understood from FIG. 7 that single addition of Si, Al or anintermetallic compound containing Si or Al do not achieve significantcontractibility with the progress of sintering in the high temperatureregion, so that single addition of these elements and intermetalliccompounds cannot ensure the desired characteristics. TiH achievesexpansion in the low temperature region and contraction in the hightemperature region so that it ensures the desired characteristicsrequired in the invention. The amounts of expansion and contraction canbe controlled by controlling the amounts of these additives or by addingAl or Si in the form of a master alloy or compound (see FIGS. 6 and 7).

The reason why Si or Al exerts expansibility is considered to be thatthey stabilize the β phase of the Cu--Sn materials. This conforms to thefact that the peritectic temperatures of the Cu--Si materials and Cu--Almaterials are observed in the higher temperature region according to theconstitution diagram. It is also conceivable that TiH achievesexpansibility because of its ability for stabilizing the β phase of theCu--Sn materials.

The effect of combinational addition of TiH--Al and that of TiH--Si!

Al or Si were respectively added in combination with TiH to preparemixture materials. The weight percentages of the elements in eachcomposition are enumerated in Table 3. The dimensional change rate of asinter produced from each mixture material was measured. FIGS. 8, 9 and10 show the results of the measurements.

                                      TABLE 3                                     __________________________________________________________________________    Cu20Sn SnAt                                                                             TiH                                                                              Al NiAl                                                                             Ni.sub.2 Al.sub.3                                                                 Fe10Al                                                                            Si                                                                              TiSi                                                                             Mn Ni Pb                                      __________________________________________________________________________    1 25   5.0                                                                              1.0                                                                              0.5                      5.0                                     2 25   5.0                                                                              2.0                                                                              0.5                      5.0                                     3 25   5.0                                                                              1.0   3.0                   5.0                                     4 25   5.0                                                                              1.0      3.0                5.0                                     5 25   5.0                                                                              1.0          3.0            5.0                                     6 25   5.0                                                                              2.0              0.3        5.0                                     7 25   5.0                                                                              2.0              0.3     0.5                                                                              5.0                                     8 10   0  6.0                                                                              2.0                      5.0                                     9 10   0  6.0   3.0                   5.0                                     10                                                                              10   0  6.0   6.0                   5.0                                     11                                                                              10   0  6.0              1.0        5.0                                     12                                                                              10   0  6.0                1.0      5.0                                     13                                                                              10   0  6.0                   1.0   5.0                                     14                                                                              10   0  6.0                      1.0                                                                              5.0                                     __________________________________________________________________________

It is understood from the examples of Al addition (see FIG. 8), when Alin the form of an intermetallic compound was added in combination withTiH, the expansibility of the sinter in the low temperature region wassignificant. This allows a large clearance between the bore of thebottom-closed tubular body and the outside diameter of the thin-walledtubular compact body, which leads to less strict process control in theproduction line and a loose tolerance in dimensioning the diameter ofthe bore. Consequently, cost reduction and improved bonding quality canbe achieved.

The preferable lower limit amount of Ti is about 0.2 wt %. The reasonfor this is that the effect of Ti can be enhanced by controlling theamount of Si, Al or an intermetallic compound containing Si or Al. Thisis obvious from the case where 3 wt % of Fe10Al alloy and 0.5 wt % ofTiH are added in combination. In this case, the behavior of the sinterchanges from expansion in the low temperature region to significantcontraction in the high temperature region.

The preferable lower limit amount of Si and that of Al are 0.1 wt %respectively, for the reason that the desired effects of addition of Si,Al or an intermetallic compound containing Si or Al can be obtained withthis amount or more. Their preferable upper limit amounts are 3.0 wt %,because the occurrence of excessive expansion requires excessivecontraction in the high temperature region and makes it difficult toachieve the desired compactness.

The effect of addition of pure Al and the aim of addition of compounds!

When adding Al in the form of pure metal powder, Al is more likely to beaffected by the sintering atmosphere (i.e., more liable to oxidation),causing excessive expansion in the low temperature region and making itdifficult to achieve densification in the high temperature region.Therefore, it is conceivable to add Al in the form of a thermally stableintermetallic compound such as NiAl or FeAl. According to this concept,the effect obtained by high-melting-point intermetallic compounds suchas Ni--Al compounds and Fe--Al compounds can be also expected byintermetallic compounds such as Cu--Al, Mn--Al, Co--Al and Cr--Al whichare close to Ni group and Fe group. Therefore, addition of such anintermetallic compound conforms to the principle of the invention. Whenusing an Al intermetallic compound, the amount of Al added is obtainedby calculating the Al content of the intermetallic compound. The amountof Ni, Fe, Co, Cr or Mn contained in the intermetallic compound usedshould be within the specified range for the invention.

When adding Al or Si in combination with TiH, it is desirable to addthem in the form of a master alloy powder containing Ti--Al or Ti--Si.

The lower limit amount of Sn and the function of Pb!

FIGS. 7 and 8 show the effect of addition of Sn and Pb to Cu--6Ti. Inconsideration of the effect, the lower limit amount of Sn is about 2 wt%. Addition of 10 wt % of Pb ensures contraction in the high temperatureregion but about 2 wt % of Sn is necessary when taking into account thebonding ability of the copper-base material relative to iron (theexpansibility of Si and Al). FIG. 10 shows the effects of addition ofvarious alloy elements to the base material containing Sn in an amountcorresponding to its lower limit and Ti in an amount substantiallycorresponding to its upper limit. As seen from this figure, the effectsof addition of Si, Al or an intermetallic compound containing Si or Alconforms to the principle of the invention.

The effect of Ni!

The coefficients of contraction of the sinters were measured in the sameway as described above, while the amount of Ni being varied. FIG. 11shows the results of the measurements. It is understood from FIGS. 11and 6 that single addition of Ni or Co gives virtually no effects on theexpansibility.

The coefficients of contraction of the sinters formed by adding theadditives in other examples were measured in the same way as describedearlier. FIGS. 12, 13, 14 and 15 show the results of the measurements.As seen from these graphs, when adding Ni in combination with Si, theexpanding characteristics of Si is prevailing in the low temperatureregion and densification is significant in the high temperature region.

FIG. 16 shows the results of measurements conducted to check thecoefficients of contraction of the sinters formed by adding theadditives in other examples. It is understood from FIGS. 12, 13, 14, 15and 16 that the effect of the coexistence of Ni and Ti is notsignificant when the amount of TiH is small (see FIG. 16). It is alsounderstood from these figures that the coexistence of Ni and Ti exertsthe contraction restricting effect in the low temperature region,contributing to stable bonding and promotes compacting in the hightemperature region. Further, Ni--Ti coexistence considerably enhancesbonding strength in the interface of the steel of the bottom-closedtubular body. For example, in the case of C2 in Table 5, a remarkableeffect, that is, a shearing strength of 20 to 25 kg/mm² is achieved. Amore desirable result can be achieved by increasing the amount of Ni andTiH (FIGS. 13 and 14). The same effect can be obtained by addition ofCo.

                                      TABLE 4                                     __________________________________________________________________________    Cu20Sn SnAt                                                                             TiH                                                                              Ni Si                                                                              Al                                                                              NiAl                                                                             NiAl.sub.3                                                                        Mo Mn Cr                                                                              Co                                                                              Pb                                       __________________________________________________________________________    1 50   0  0.2                                                                              5.0                     0                                        2 50   0  0.2                                                                              5.0                     5.0                                      3 50   0  0.2                                                                              5.0                     10.0                                     4 50   0  0.2                                                                              10.0                    5.0                                      5 50   0  0.2                                                                              10.0                                                                             1.0                  5.0                                      6 50   0  2.0                                                                              10.0                    5.0                                      7 50   0  0.2                                                                              10.0 1.0                5.0                                      8 50   0  0.2                                                                              10.0   3.0              5.0                                      9 50   0  0.2                                                                              10.0          1.0       5.0                                      10                                                                              50   0  0.2                                                                              10.0             1.0    5.0                                      11                                                                              50   0  0.2   1.0                5.0                                                                             5.0                                      12                                                                              25   0  0.2                                                                              10.0                    5.0                                      13                                                                              25   0  0.2                                                                              5.0                     5.0                                      14                                                                              25   0  0.2                                                                              5.0                                                                              1.0                  5.0                                      15                                                                              25   0  2.0                                                                              5.0                     5.0                                      16                                                                              25   0  0.2                                                                              5.0    3.0              5.0                                      17                                                                              25   0  0.2                                                                              5.0                 1.0 5.0                                      18                                                                              25   5  1.0                                                                              2.0                     5.0                                      19                                                                              25   5  1.0                                                                              3.0                     5.0                                      20                                                                              25   5  1.0                                                                              2.0                                                                              0.5                  5.0                                      21                                                                              25   5  1.0                                                                              3.0                                                                              0.5                  5.0                                      22                                                                              25   5  0.7                                                                              2.4                                                                              0.2                  5.0                                      23                                                                              25   5  0.7                                                                              2.4                                                                              0.7                  5.0                                      24                                                                              25   5  0  2.0                                                                              1.0           1.0    5.0                                      25                                                                              25   5  0  3.0                                                                              1.0           1.0    5.0                                      __________________________________________________________________________

                                      TABLE 5                                     __________________________________________________________________________    Cu20Sn* Cu30Zn                                                                             Sn**                                                                             TiH                                                                              NiAl Si                                                                              Al                                                                              Ni                                                                              Ti.sub.5 Si.sub.3                                                                 Pb C(Gr)                                                                            Mg                                    __________________________________________________________________________    C 1     50.0 6.0                                                                              0.2               5.0                                         C 2     50.0 6.0                                                                              0.2                                                                              3.0            5.0                                         C 3     50.0 6.0                                                                              0.2     0.3       5.0                                         C 4     50.0 6.0                                                                              0.2       0.5     5.0                                         C 5     50.0 6.0                                                                              0.2         2.0   5.0                                         C 6     50.0 6.0                                                                              0.2           2.0 5.0                                         C 6'    50.0 6.0                                                                              0.2               5.0                                                                              0.2                                      C 7     50.0 6.0                                                                              1.0               5.0                                         C 8     50.0 6.0                                                                              1.0                                                                              3.0            5.0                                         C 9     50.0 6.0                                                                              1.0     0.3       5.0                                         C10     50.0 6.0                                                                              1.0       1.0     5.0                                         C11     50.0 6.0                                                                              1.0         2.0   5.0                                         C12     50.0 6.0                                                                              1.0           2.0 5.0                                         C13     50.0 6.0                                                                              2.0               5.0                                         C14     50.0 6.0                                                                              2.0                                                                              3.0            5.0                                         C15     50.0 6.0                                                                              2.0     0.3       5.0                                         C16     50.0 6.0                                                                              2.0       0.5     5.0                                         C17     50.0 6.0                                                                              2.0         2.0   5.0                                         C18     50.0 6.0                                                                              2.0           2.0 5.0                                         C18'    50.0 6.0                                                                              2.0               5.0   0.5                                   C19                                                                              24 + 3.6                                                                           33.0 -- 0.2               5.0                                         C20                                                                              24 + 3.6                                                                           33.0    0.2                                                                              3.0            5.0                                         C21                                                                              24 + 3.6                                                                           33.0    0.2     0.3       5.0                                         C22                                                                              24 + 3.6                                                                           33.0    0.2       0.5     5.0                                         C23                                                                              24 + 3.6     0.2         2.0   5.0                                         C24                                                                              24 + 3.6     0.2           2.0 5.0                                         C24'                                                                             24 + 3.6     0.2                                                                              Mn;1       2.0 5.0                                         C25                                                                              24 + 3.6     1.0               5.0                                         C26                                                                              24 + 3.6     1.0                                                                              3.0            5.0                                         C27                                                                              24 + 3.6     1.0     0.3       5.0                                         C28                                                                              24 + 3.6     1.0       2.0     5.0                                         C29                                                                              24 + 3.6     1.0         2.0   5.0                                         C30                                                                              24 + 3.6     1.0           2.0 5.0                                         C30'                                                                             24 + 3.6     1.0                                                                              N2A3;6                                                     __________________________________________________________________________     *(Cu20Sn;24% + Cu33Sn;3.6%)                                                   **(Sn;5% + Cu33Sn;3%)                                                    

When adding Ni in a large amount such as 10 wt %, the aboveexpansion/contraction effect can be achieved even when the amount of TiHis 2 wt %. Therefore, the upper limit amount of TiH may be about 3 wt %.

Functional explanation of the effect of Ni addition!

A study of the effect of Ni addition has shown that single addition ofNi gives virtually no effects on expansion and contraction but whenadding Ni in combination with Si or Al, the expansibility of Si or Al isdeveloped in the low temperature region while densification is achievedin the high temperature region as Ni combines with Si or Al to form acompound in the high temperature region, decreasing the expansibility ofSi or Al significantly to promote shrinkage during sintering. Thiseffect is considered to be substantially the same as that of TiHaddition. It has been verified that exactly the same effect can beobtained by Co addition. Almost the same effect can be anticipated byaddition of an element such as Mn, Mo or W which has superior ability tocombine with Si or Al to form a compound. As Ni can exert its effectwhen added in amounts which are five times the amount of Si or Al, thelower limit amount of Ni may be about 0.5 wt %. In view of cost, theupper limit amount of Ni may be about 20 wt %. For achieving asatisfactory, stable effect, the preferred amount of Ni is in the rangeof from 2 wt % to 5 wt %.

The functions of other alloy elements!

FIG. 17 shows the dimensional change rates of the sinters formed byadding the additives in the examples shown in FIGS. 13, 14, 15 and inother examples. It is understood from FIG. 17 that Cr and Mn can be usedin the invention as they meet the requirements of the principle of theinvention. Cr exerts expansibility in the low temperature region andcontractibility in the high temperature region similarly to Si and TiH,and it is therefore understood that Cu has the same effect as Si, Al andTiH.

The effect of Zn addition!

FIG. 18, 19, 20, 21 and 22 show the dimensional change rates of thesinters formed by adding the additives in other examples.

It is understood from these graphs that when adding Zn alone, Zn exertsits expansibility in the low temperature region and sequentially exertsconsiderable contractibility in the high temperature region. The reasonfor this is that Zn has the same function as Si and Al in terms of thestabilization of the β phase in the C--Zn materials (FIG. 18).

When adding Zn in combination with Si or Al, expansibility in the lowtemperature region is enhanced by the coexistence of Zn and moreincreased as the amount of Zn increases. The coexistence of Zn has theeffect of achieving contractibility in the high temperature regionwithout use of Ti or Ni when the amount of Al is in a certain range.These effects are inherent to Zn and distinct from the effects of otheradditives (FIGS. 18, 19, 20, 21, 22). Although the degree to which Zncan obtain desired effects differs from those of other additives,combinational addition of Zn is regarded as a useful means in view ofthe increased degree of freedom in the range of alloy compositions. Ni,graphite and Mg have no considerable difference in behavior between thecase where each of these elements was added in combination with Zn andthe case where each element was added without Zn. It is thereforeunderstood that Ni, graphite and Mg, basically, do not interact with Znto a noticeable extent.

The lower limit amount of Zn may be 0 wt %, because expandabilityincreases in proportion to the amount of Zn at low temperatures, forexample, when Zn is added together with 0.5 wt % of Al as shown in FIG.18.

The upper limit amount of Zn may be about 30 wt % in view of thedifficulty in molding when Zn is added as a master alloy. The amount ofZn affects the expanding temperature of the sinter as set forth above,and therefore the preferable amount of Zn should be adjusted inconjunction with the amount of other additives such as Sn, Pb and TiH.

When the amount of Zn exceeds 20 wt %, it is desirable in considerationof the evaporating characteristic of Zn to sinter the green compactunder a pressurized atmosphere in the presence of inert or reducing gassuch as N₂ gas, which gives the effect of increasing sintered density inthe high temperature region.

Expansion in the low temperature region required for joining!

FIGS. 23, 24 and 25 show the dimensional change rates of the sintersformed by adding the additives in other examples. As seen from FIGS. 23to 25, the green compacts each containing a powder behave in variousexpanding patterns with rising temperature. The cause of the expandingbehavior was investigated, using Hansen's constitution diagram. It isconceivable from the investigation that the generation of theintermetallic compound phases called η, ε, γ and β phases concerns theexpanding behavior and that the emergence of a liquid phase due to thedisappear of a compound changes the behavior of the material fromexpansion to contraction. Therefore, the emergence pattern ofexpansion/contraction varies according to Sn sources. For example, inthe case of Cu--33Sn, great expansion (730° C.) due to the emergence ofthe γ phase and very small expansion due the emergence of the β phaseare admitted. In the case of Cu--20Sn, expansion due to a transitionfrom the δ phase to the γ phase and β phase is admitted.

The results of Sn addition in various ratios and combinations are summedin the graph of FIG. 26. As seen from this graph, expansion reaction dueto the emergence of the β phase in the high temperature region, which isvery useful for joining, is very small in amount and even smaller thanthe volume of thermal expansion (coefficient of thermalexpansion=18×10⁻⁶) in all of the examples shown in FIG. 26, and it istherefore found that great expansion required for joining cannot beobtained by simply changing the Sn source. In the graph of FIG. 26,solid line (1) represents the thermal expansion/contraction curve ofsteel (SCM440H) and solid line (2) represents the thermalexpansion/contraction curve of steel when taking into account theclearance (50 μm per φ25 mm) between the outside diameter of thethin-walled tubular compact body (Cu-base pipe material) and the bore ofthe bottom-closed tubular body. It is understood, from the comparisonbetween the curve representing each example and the curves (1) and (2),that the expansion for achieving the required bonding ability cannot beobtained by addition of Sn. Of these examples, Cu--33Sn is the mostsuitable. In the case of Cu--20Sn, the amount of Cu20Sn powder is solarge that contraction due to solid phase sintering is not negligibleand the new emergence of the β phase cannot be expected at temperaturesequal to and more than the peritectic temperature of the Cu--Snmaterial. Therefore, expansion necessary for joining cannot be expectedfrom addition of Cu--20Sn.

In should be noted that in the above examples, sintering was performedby heating each copper-base powder material according to its compositionto a temperature at which satisfactory compactness (preferable relativedensity=85% or more) could be achieved.

The principle of the invention is to obtain expansion in the hightemperature region which is useful in joining. In other words, theemergence of a liquid phase necessary for joining and the new emergenceof the β phase are developed by using the alloying technique andutilized in joining. By way of example, Cu20Sn alloy powder was used asan Sn source to prepare a base material in which expansion due to the βphase does not occur. 3 wt % of NiAl and 1 wt % of TiH were then addedto this base composition thereby to prepare an alloy. The thermalexpansion/contraction curve of this alloy is graphically shown. It isunderstood from this characteristic curve that extremely remarkableexpansion can be caused by the emergence of the β phase, which isgreater than the expansion of steel indicated by the characteristiccurves (1) and (2) so that satisfactory bonding ability can be ensured.

The volume of expansion necessary for joining has been investigated,using the graph of FIG. 8 as data. The result of the study is shown inFIG. 27. This graph was prepared based on the measurement results shownin FIG. 26 and based on the facts that the coefficient of expansion ofthe Cu-base sintering materials is 18×10⁻⁶ when they are expanded from athermal contraction state (cooled state) and that the dimensional changerate of the Cu--10Sn--5Pb materials is -1.2%. When the clearance betweenthe thin-walled tubular compact body and the bore of the bottom-closedtubular body is zero, the expansion volume obtained by addition of analloy element is 0.5% of the parent alloy. When the clearance is 50 μm,sinter-joining is substantially possible by an expansion volume of about0.8% (per φ25 mm). Although the reason for this conforms to the resultsdescribed above, it is desirable, in consideration of the stability ofjoining and variations in processing, to obtain an expansion volumeequal to or more than 1% of the volume of the base alloy. If the amountof a component of the steel (for example, carbon content) is changed,the α/γ transformation point of the steel is changed as well and it istherefore necessary to take the expansion volume of the Cu-base pipematerial into account. This problem can be however solved by controllingthe expansion volume of the Cu-base sinters beforehand by adding analloy element such that the contraction volume at the α/γ transformationpoint can be compensated by an expansion volume of about 0.25%.Specifically, the expansion volume is increased by 0.25% of the basematerial so that the expansion volume required is 1.05%.

Investigation of expansive alloy elements!

When adding an element which stabilizes the β phase in the Cu--Sn alloyconstitution diagram, the β phase newly appears to a considerable extentfollowing the emergence of a liquid phase so that great expansionreaction can be expected in this reaction area. To achieve suchexpansion reaction, alloy elements to be added are selected so as tomeet the following two conditions.

(1) Eutectic and peritectic alloy elements, which stabilize the β phasein Cu containing alloys such as Cu--Sn alloys, are selected formHansen's constitution diagram.

Examples of the alloy elements which satisfy the above requirement areAl, Si, Ga, Be, In, Sb and Zn. Of these alloy elements, Al is the mosteffective in view of the β phase stabilizing effect, and Si and Zn arealso suitable elements from a practical viewpoint. The essential factorfor the expansion reaction is presumably the precipitation of the βphase caused by the reaction of the expansive elements with a liquidphase generated during sintering. Taking this into account, it can beeasily presumed that Al, Si and Zn may be added in the form of acompound such as NiAl or in the form of a master alloy. The effect ofGa, Be, In and Sb is basically the same as that of Al, Si and Zn.

(2) In order to stabilize the β phase similarly to the requirement (1),even if the β phase does not exist in Cu alloys, the alloy elementsshould have at least the BCC crystal structure identical with the βphase and form a solid solution with Cu to some extent.

Examples of such alloy elements are Ti, Zr and Fe. It should be notedthat these elements have a smaller expansion effect than the elementslisted in (1).

Investigation of elements capable of promoting densification in the hightemperature region!

Since addition of an expansive element retards the densification of thesinter in the high temperature region, causing undesirable materialcharacteristics, it is necessary to promote densification within aspecified range of temperature.

(1) In order to promote densification, the forms of precipitates may bechanged so that the β phase stabilizing function of the expansiveelement such as Si or Al can be restricted at temperatures equal to andmore than 850° C. For example, the β phase may be changed to Ni3Si,TiAl, Ni3Ti or TiSi and C may be changed to TiC.

In view of the above principle, elements which form a stabileintermetallic compound when mixed with an expansive element such as Ti,Ni, Fe, Mn, Cr or Co can be used for promoting densification in the hightemperature region.

(2) Basically, the sintered density of the sinter can be increased byincreasing the quantity of a liquid phase during liquid-phase sintering.In view of this fact, Pb, Zn, P, Ag, In and many other elements areconceivably used, but the above elements are more practical. It isunderstood from the above explanation that Ti and Zn have an expandingfunction as well as a contracting function at high temperatures.

As has been described above, one of the features of the inventionresides in that a copper-base material is expanded at low sinteringtemperatures so as to be brought into pressure contact with an iron-basematerial for joining and contracted at high sintering temperatures toobtain compactness necessary for forming a sinter, as graphically shownin FIG. 28. In this method, bonding ability can be increased bydecreasing the temperature rising rate in sintering in the lowtemperature region and or by heating the material at the sametemperature for a specified time in the low temperature region. Thescope of the invention includes sinter-joining in which the copper-basematerial is not brought into pressure contact with the iron-basematerial, but simply brought into contact with the iron-base material.This case provides the advantage that when the copper-base material isjoined to the iron-base material by sinter-ing at low temperatures, thecontraction of the copper-base material does not cause a shift of thecopper-base material from the iron-base material in an unexpecteddirection.

The sinter-joining method and the sintered composite member according tothe invention are applicable, for example, to the manufacture ofcylinder blocks.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

We claim:
 1. A sinter-joining method for joining a copper-base materialto an iron-base material, the method comprising the steps of:(a) heatingthe copper-base material, which is composed of at least three componentsincluding at least one of: (i) at least one metal and (ii) at least onesemi-metallic element which has ability to give expansibility, incontact with a bore of the iron-base material at temperatures equal toand higher than 600° C. for a specified time so that the copper-basematerial expands and joins to the iron-base material, and (b) furtherheating the copper-base and iron-base materials at temperatures equal toand higher than 800° C. to increase the compactness of the copper-basematerial.
 2. A sinter-joining method according to claim 1,wherein thebore of the iron-base material has a tubular shape and the copper-basematerial is a tubular copper-base member having an outside diameter thatis substantially equal to or slightly smaller than the diameter of thebore of the iron-base material, and wherein the tubular copper-basemember and the iron-base material are heated at a temperature of atleast 600° C. while the tubular copper-base member being inserted in thebore of the iron-base material.
 3. A sinter-joining method according toclaim 1 or 2,wherein the copper-base material contains a Cu--Sncomponent and at least one of a metal and a semi-metallic element whichstabilizes the β phase of the Cu--Sn alloy or a phase similar to the βphase of the Cu--Sn alloy, as an element for promoting expansibility. 4.A sinter-joining method according to claim 3, wherein said element thatstabilizes the β phase or phase similar to the β phase is at least oneelement selected from the group consisting of Al, Si, Ga, Be, In, Sb,Zn, Ti, Zr, Mn, Cr, and Co.
 5. A sinter-joining method according toclaim 3, wherein the copper-base material contains an element whichinhibits the stabilizing function of the element for stabilizing the βphase or phase similar to the β phase.
 6. A sinter-joining methodaccording to claim 5, wherein said element that inhibits the stabilizingfunction of the element for stabilizing the β phase or phase similar tothe β phase is at least one element selected from the group consistingof Ti, Pb, Zn, P, Sb, Ag, In, Ni, Co, Mn, Fe and Cr.
 7. A sinteredcomposite member, comprising a copper-base material and an iron-basematerial, said copper-base material and said iron base material beingsinter-joined,the sinter-joining includes: (a) the copper-base materialbeing heated in contact with a bore of the iron-base material attemperatures equal to and higher than 600° C. for a specified time sothat the copper-base material expands and joins to the iron-basematerial, and the copper-base material being composed of at least threecomponents including at least one of: (i) at least one metal and (ii) atleast one semi-metallic element which has ability to give expansibility,and (b) the copper-base and iron-base materials being further heated attemperatures equal to and higher than 800° C. to increase thecompactness of the copper-base material.
 8. The sintered compositemember according to claim 7, wherein the bore of the iron-base materialhas a tubular shape and the copper-base material is a tubularcopper-base member having an outside diameter that is substantiallyequal to or slightly smaller than the diameter of the bore of theiron-base material, andwherein the tubular copper-base member and theiron-base material are heated at a temperature of at least 600° C. whilethe tubular copper-base member being inserted in the bore of theiron-base material.
 9. The sintered composite member according to claim7 or 8, wherein the copper-base material contains a Cu--Sn component andat least one of a metal and a semi-metallic element which stabilizes theβ phase of the Cu--Sn alloy or a phase similar to the β phase of theCu--Sn alloy, as an element for promoting expansibility.
 10. Thesintered composite member according to claim 9, wherein said elementthat stabilizes the β phase or phase similar to the β phase is at leastone element selected from the group consisting of Al, Si, Ga, Be, In,Sb, Zn, Ti, Zr, Mn, Cr, and Co.
 11. The sintered composite memberaccording to claim 9, wherein the copper-base material contains anelement which inhibits the stabilizing function of the element forstabilizing the β phase or phase similar to the β phase.
 12. Thesintered composite member according to claim 11, wherein said elementthat inhibits the stabilizing function of the element for stabilizingthe β phase or phase similar to the β phase is at least one elementselected from the group consisting of Ti, Pb, Zn, P, Sb, Ag, In, Ni, Co,Mn, Fe and Cr.